In the machining of machine parts such as gears, journals, and the like it is obviously very important to machine them with surfaces that conform absolutely to the desired shape, whether this be with respect to a plane, a center of curvature, or an imaginary nonplanar curve. Normally the various grinding or machining tools act on the workpiece sequentially, that is the workpiece is moved from tool to tool. In addition it is standard practice to rechuck the workpiece for each different tool. Although it is possible to rechuck with considerable accuracy, such an operation wastes time, and the small errors created with each rechucking are cumulative, leading frequently to an unacceptable total deviation from the desired shape.
Accordingly it has been suggested in German patent document No. 2,911,345 filed by M. Onoda, Y. Nakajima, and S. Iwata with a claim to a Japanese priority date of Mar. 22, 1978 to provide inner-surface and outer-surface grinders immediately adjacent one another on a common machine bed. An annular workpiece can thus be machined on both its inner and outer surfaces simultaneously by this machine.
The problem with this type of arrangement is that many workpieces, such as tubular shaft journals, not only must be machined internally and externally, but this machining must be done at both ends. Thus even in the system described in this German patent document it is necessary to dechuck, reverse, and rechuck the workpiece. This process similarly increases the likelihood of misplacing the workpiece and machining it in a later step about a center that differs from that about which the machining took place in the earlier step.